The disclosure relates to a method for re-tensioning an automatic parking brake by means of an electric motor, to a control device having a re-tensioning algorithm, and to an automatic parking brake for vehicles having a special re-tensioning method.
Automatic parking brakes (APB) usually comprise an operator control element such as, for example, a pushbutton key with which the parking brake can be locked or released. When the operator control element is activated, a control device connected thereto detects the parking brake request and actuates an actuator element such as, for example, an electric motor correspondingly in order to build up braking force at the parking brake or to release the brake.
A wide variety of different parking brake systems are known from the prior art, which also include systems in which the electric motors (with transmissions) are located directly on the wheel brakes. This design is also referred to as “motor on caliper”.
Conventional parking brakes are usually re-tensioned after a predefined waiting time. This is due to the fact, in particular, that after the stationary state of the vehicle the parking brake cools and the individual mechanical components of the parking brake shrink slightly as a result. A loss of clamping force can occur owing to such thermal relaxation. In order to continue to ensure the functional capability of the parking brake, it must be re-tensioned from time to time. For this purpose, the electric motor of the parking brake is actuated again by the parking brake control device a predefined time after the vehicle has been shut down, and the parking brake mechanism is driven automatically in the tensioning direction until the desired clamping force is restored. The re-tensioning of the parking brake is generally repeated several times. With this method, it is, on the one hand, disadvantageous that the parking brake system has to be operational for a relatively long time. On the other hand, the electric on-board power system and the individual components of the parking brake are loaded to a relatively large extent.
The object of the present disclosure is therefore to provide a method for re-tensioning a parking brake which is actuated by electric motor and to provide a parking brake system in which the re-tensioning process can be carried out significantly more efficiently.